FIG. 1 shows an arrangement for explaining a conventional technique of determining the positioning of a wire or like article (hereinafter referred to simply as wire) which is shown in, for example, the digest of technical papers, G-78, for the 1986 joint meeting of the electrical and electronic societies of Western Japan. The arrangement comprises an objective lens 1, an image pickup device (camera) 3 which converts into an electrical signal the image of a wire 5 imaged on the pickup device 3 by the objective lens 1, an image processor 4 for processing the video signal supplied from the pickup device 3, and a movable base 6 for moving the wire 5 which is placed thereon in the field of the objective lens 1.
In operation, the image of the wire 5 on the movable base 6 of which the shape is to be determined is imaged on the imaging surface at the pickup device 3 by the objective lens 1. Since the wire 5 has the shape which varies three-dimensionally, only those portions of the wire 5 which lie in the focal plane 100 determined by the distance of the imaging surface of the pickup device 3 from the objective lens 1 and the focal length of the objective lens 1, are imaged with high contrast and the remaining portions of the wire 5 are defocused. When the movable base 6 is moved up or down, different portions of the wire 5 come to lie in the focal plane 100 successively.
The video signal provided by the image pickup device 3 is applied to the image processor 4 which extracts the contrast between the image of the wire 5 and the background. For each of locations on the imaging surface, (called "pixels" when digital image processing is to be provided), the position of the movable base 6 where maximum contrast is formed at that location is determined from the image data obtained through the image processing in the processor 4, and the thus determined positions of the base 6 are stored. This processing is repeated with the base 6 being moved in small steps in either one of the directions indicated by arrows in FIG. 1. After the completion of the processing over the range of movement of the base 6, the height of the wire 5 or the levels of respective portions of the wire 5 can be calculated from the values of the stored positions of the base 6.
The above-described method for determining the shape of a wire or like article is time-consuming, because the movable base 6 must be moved in small steps and for each position thereof, imaging and image processing must be made. Another disadvantage of this method is that because it is time-consuming, the method cannot determine the shape of the wire 5 when it changes in shape in time or when it is moving.
One example of apparatus for detecting a wire or like article is shown in FIG. 2. The apparatus is a well-known wire bond inspecting apparatus disclosed in unexamined Japanese Patent Publication No. SHO 60-49212. This apparatus comprises a rotary base 41. An IC 42 to be inspected is placed on the base 41. Two TV cameras 43 and 44 are mounted above and diagonally with respect to the base 41. The cameras 43 and 44 are in mutually opposing positions with the base and, hence, the IC thereon being intermediate between them.
The IC 42 is placed in position on the rotary base 41, and it is imaged simultaneously on the two TV cameras 43 and 44. FIG. 3 shows two images provided by the apparatus of FIG. 2. From these two images, the lateral displacement of a wire 45, .DELTA.l, from a reference line is determined from an equation .DELTA.l=(A-B)/2sin .alpha. as shown.
In the arrangement shown in FIGS. 2 and 3, an article is picked up in diagonal directions by the two TV cameras, and the wire shape is determined from the parallax of corresponding portions of the wire derived from the two images. Accordingly, in case that a number of wires are densely arranged or wires of like shape are spanned in parallel with each other, it is difficult to detect the same desired wire in the two image, or wires of interest to be inspected may be hidden behind adjacent wires so that useful inspection cannot be made.